In 2018 a paper was published in Ultrasound in Medicine and Biology showing absence of the second systolic peak in patients with severe sepsis.
- de Goede A.A., Loef B.G., Reidinga A.C. and Schaafsma A. Fluid resuscitation in septic patients improves systolic but not diastolic middle cerebral artery flow velocity. Ultrasound in Medicine and Biology 201; 43: 2591-2600). The paper can also be found at: sciencedirect.com
These findings illustrate how important it is to discriminate a first and second systolic phase in pulsatile signals such as arterial blood pressure or intra arterial blood flow velocity.
The graph above shows (age corrected) Z-scores for a group of 16 patients before (red) and after (yellow) fluid resuscitation. All patients had high Z-scores for all parameters before as well as after fluid resuscitation. Fluid resuscitation increased the Sys1 and Sys2 components, allowing a slight decrease in HR.
These high Z-scores for Sys1, Sys2 and Dias@560 may implicate a diffuse loss of cerebral arteriolar resistance, either due to low blood pressure or because of circulating endotoxins.
The blood flow velocities measured by TCD are complex signals but can give instantaneous information about cerebral hemodynamics. Neuromon B.V. aims to disclose this information in a meaningful way to physicians for rapid diagnostic and therapeutic purposes. At the beginning of 2018 Neuromon B.V. presented a novel approach for graphical representation of the middle cerebral artery flow velocity. Based upon the improved parameters Z-scores are calculated to correct for age and different variables are combined into a single radar-plot.
A Z-score expresses how many standard deviations a given measurement is above (positive) or below (negative) the value expected for a given age. Z-scores for different parameters can be combined into a radar plot. An example is give to the right: data are provided for average Z-scores during hyperventilation (red), normoventilation (green) and CO2-retention (yellow).
A. Schaafsma, A new method for correcting middle cerebral artery flow velocity for age by calculating Z-scores. Journal of Neuroscience Methods. 307, 1–7 (2018).
The background of this graphical representation is also explained in the following pamflet: TCD-NewParmCoordinates.pdf.
Neuromon has prepared 6 presentations of 8 to 13 minutes explaining the theoretical background behind the model for cardiovascular simulation. This model was originally developed in Labview™ in collaboration with Annika de Goede from the TUTwente. It was subsequently translated to C# by Neuromon. After registration, the model can be downloaded from the web page.
The model of cardiovascular simulation should be seen as an illustration of theoretical concepts in cardiovascular physiology. It includes the CNS ischemic response, the theory of arterial acceleration and cardiovascular reflexes such as auto regulation, the baroceptosr reflex the chemoreceptor reflex and the Bainbridge reflex.
Incorporating different physiological responses into a single computer simulation helps to understand the complex interplay of all these responses combined. A computer simulation should be seen as an illustration of the theory. It is based upon simple mathematical rules that joined together become a system of high complexity. A model as this, however, can never live up to the complexity of cardiovascular physiology in real life.
The 6 presentations can be found on the web page for theoretical background.
Alternatively, a link to the first presentation can be found below.
Recently, a video was released discussing how the theory of arterial acceleration is part of the ongoing scientific quest for a better understanding of cardiovascular physiology. This quest started with Galen in the 2nd century, is greatly furthered by Harvey in the 17th century as well as by various investigators at the end of the 19th century. The theory of acceleration adds to conceptual thinking about the role of the arterial system in cardiovascular physiology. It challenges a too simplistic view on arterial blood pressure.
This app intends to bridge the gap between middle cerebral artery flow velocity parameterisation and clinical interpretation. Basically, sys1, sys2, dias@560 and HR are converted to so-called Z-scores that correct for the effects of ageing.
Based upon published observations the Z-scores are used for clinical interpretation. Of course, Neuromon BV cannot take the responsibility for clinical decision making and the NMA app should only be seen as support in the process. Treating physicians should always remain vigilant and not use information from the NMA alone to interpret the clinical condition of a patient. Nevertheless, the NMA module brings a new approach to patient assessment on the ICU based upon a new philosophy on cardiovascular physiology.
Find your NMA in the Appstore via this link NMA or alternatively by searching "NMA TCD".
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